1. Field of the Invention
The present invention relates to a packing method for a compressed package of filter tow or filament, and more particularly to a method of packing tow for cigarette filters. Further, the present invention relates to a packing method for a package obtained by packing compressed filament or the like with a bonding method such as sealing.
In particular, the present invention relates to, a packing method for a package obtained by packing filter tow made of cellulose acetate, the content of which is compressed with pressing means such as a press, including decreasing rebound internal pressure caused by the compression of the content and then making an entire peripheral seal, dot seal, bonding or the like to control the rebound force.
2. Description of the Related Art
Fiber, tow, filament and the like have a low bulk density. Filter tow made of cellulose acetate, for example, has a low bulk density of approximately 100 kg/m3. Considering transport efficiency and in-house handling during processing into a cigarette filter, filament is compressed with pressing means, such as a press, to increase the bulk density to 300 to 600 kg/m3 at the time of packing. This type of package is referred to as bale (tow bale).
A packaging method and a packaging device for filter tow bales are described in WO-A2 02/32238 as a bale compressing device (bale packing device). According to the technology described in this document, a manufactured filter tow is in a form of a continuous fiber. That is, it is advantageous in terms of production efficiency to use a long filter tow for processing into a filter because a manufacturing device for a cigarette filter operates at a high speed of 400 to 600 m/min. Thus, the length of the filter tow needs to be long as described above. In the case of usual monofilament having a diameter of 3 D (denier, applied hereinafter), a tow band of integrated tow filaments includes 10000 to 13000 monofilaments aligned. Therefore, the filament and the tow band of the integrated filaments have a length of 15 km in the case of a tow band of 30000 D and a tow bale weight of 500 kg, for example. In the bale-packing and bale-compressing device described in the above-mentioned WO-A2 02/32238, a tow band having this length is fed into a so-called filling container (also referred to as a filling box or a compression box). In this state, the filter tow in the filling container is extremely bulky.
Therefore, the filling box has a height as high as 6 m, for example. It is naturally extremely inefficient to transport or store such box, and hence it is required that the filter tow fed into this filling box be compressed to a size suitable for transportation and storage in a common technology. Thus, in a common technology, in the subsequent process, the content filled in the filling container is pressurized vertically and compressed. The compression force is extremely large and is a pressure of several hundred tons, approximately 300 to 600 t in general, and 500 t for example. After this compression, in a state under the compression stress, the compressed filter tow is packed with a packaging material (which may be referred to as a packing material). These packaging materials include a cardboard, a corrugated cardboard, a non-woven cloth, a plastic film, a film include in synthetic fiber and the like. These packaging materials cover the respective surfaces of the compressed filter tow. These packaging materials use a package form in which the tow bale is strapped with straps made of steel or plastic (these are referred to as binding straps) so as not to rupture by the rebound force of the filter tow bale when the pressure applied onto the compressed filter tow is removed. That is, the remaining rebound internal pressure of the filter tow is held by the binding straps.
As described above, a press compression pressure of a highly compressed bale can reach 5000 kPa (500 t/m2) at the maximum and is not lower than 1000 kPa (100 t/m2) even if the compression pressure is low.
Therefore, as described above, even after the packing, a reboundpressure (expansion force of bale) of 20 to 400 kPa remains in the package of the filter tow due to the stress against the compression. Such a rebound pressure has been conventionally well known. JP-A 53-87890 (Patent Document 1), for example, discloses that “there is an internal pressure of at least 0.2 daN/cm2 (20 kPa), and there is a considerably high pressure of up to approximately 3.3 daN/cm2 (330 kPa) in a short time” (page 2, lower right column, line 20 to page 3, upper left column, line 1).
In order to make a package that can withstand such a rebound internal pressure, in prior arts, filter tow package is strapped by a binding strap made of a metal or a plastic strap as described above. The binding strap integrates the packaging material and the pressed bale. In prior arts, packaging materials for the side part, the top and the bottom of a usual package are integrated by a binding strap. As a result, the tow bale is prevented from being ruptured, but portions other than the portion of the binding strap which cannot be expanded will be expanded with expansion of the tow bale.
As a result, the binding strap bites into a surface layer of the filter tow and causes constriction in the tow bale. When the filter tow is taken out as a continuous fiber, the filter tow substantially attaches to itself in that portion, and when the attached portion is pulled, it is likely that the filter tow band is fractured because the filter tow is partially compressed by a high pressure in the constriction portion. Further, it is possible that the binding strap is cut off when unpacked, cut-off pieces of the binding strap are sprung away and a worker might be injured.
Therefore, it has been studied to omit the binding strap in packaging. The above-mentioned Patent Document 1, for example, discloses in order to solve the problem of the filter tow strapping with the strap, a package obtained by packaging a compressed filter tow by a packaging material and bonding the packaging material with an adhesive applied to the packaging material. In this case, the rebound pressure of the tow bale is applied to the packaging material.
Thus, according to the above-mentioned Patent Document 1, the package is described such that the compressed filter tow is wrapped inside with a laminate of aluminum-deposited PP and paper and outside with a corrugated cardboard bonded with a solvent type adhesive, specifically a chloroprene rubber solvent-type adhesive.
As described above, with the above-mentioned Patent Document 1, an expansion force of the compressed bale is applied to the package. Thus, in the above-mentioned Patent Document 1, overlapping portions of the exterior package of the package are bonded to each other with an adhesive providing a shear strength of at least 0.39 daN/cm2 (39 kPa) (claims) to the bonded portion. As described above, in the above-mentioned Patent Document 1, the bonding strength of the bonded portion needs to be considerably large, and the packaging material also needs to be a special material which can withstand the expansion pressure of the bale. Thus, as in the embodiment of the above-mentioned Patent Document 1, the packaging material needs to have a multi-layered structure of an interior package made of a complex material of paper, polyolefin resin and aluminum foil and an exterior package made of cardboard.
Further, JP-A 7-215338 (Patent Document 2) discloses a technology of bonding a top part and a central part of a collecting container without an adhesive, but a planar fastener tape. In this technology, several side parts capable of upright standing surrounding an outer periphery of the collecting container and determining a boundary are provided. By means of this side part, the rebound internal pressure can be withstood without a binding strap. That is, a planar fastener is used between the side part and the collecting container on the side of this package, and the planar fastener is pressure-bonded all the time and firmly bonded by the rebound internal pressure of the collecting container. On the other hand, the side part is required to have rigidity and strength that can withstand the rebound internal pressure of the collecting container, elaborate packing is required, and a cost is raised. Thus, these packages cannot be applied for one-way packing and can be used only in a range that these packing materials can be recovered and reused.
JP-A9-508880 (Patent Document 3) discloses a package sealed with a plastic film or sheet. In accordance with the description of Patent Document 3, 3-sheet packaging with 3 sheets for a top part, a bottom part and a body part, respectively, will be described below. That is, in the case of this packaging, a packing form is disclosed in which a packaging material segment provided so as to wrap the side part is drawn out for a required length from a roll of the packaging material, closed at an end portion and welded by surrounding a pressed bale so as to form a tube closed vertically at a bottom part and a top part. And it is described that the binding strap can be omitted with this packing form. After the bale is compressed in this package, the body part is formed by wrapping with a film, and the bottom part and the top part need to be set in a bale compressing device in advance.
Patent Document 3 describes that the packaging materials of the top part and the body part, and the bottom part and the body part, may be heat-sealed on the entire periphery (page 23, lines 2 to 6) or may be dot sealed in a stripe shape or a point shape at the bonded spot. In the case of dot seal, it is described that the seal can be peeled off relatively easily by hand or using an appropriate machine to be released (page 21, lines 27 to 37). And by employing this packaging form, it is described that even after the pressing force applied to the pressed bale is removed, the expanding bale force is withstood and additional reinforcement by a band or a similar tool is not needed (page 19, lines 28 to 32).
With the technology described in Patent Document 3, the bale is expanded after the pressing force is removed, and the expansion force in that case is also applied to the bonded spot. Therefore, the adhesion strength at the bonded spot needs to be raised to such a degree that can withstand the expansion pressure, and there is a possibility that the bonded spot might be released at the time of expansion.
GB-A 1280932 (Patent Document 4) discloses a bale package containing two parts: a relatively deep bag-base part and a relatively shallow bag cap part. The both bags are stocked and supplied to a bale press. The relatively shallow cap part forms a bottom part of the bale, while the relatively deep base part forms a top part and a body part. Into the base part, a bulky tow is pushed in and compressed by a plunger. The bale in which the base part and the cap part are continuously welded (sealed) (sealed on the entire periphery) is disclosed (column 2, lines 14 to 59).
In the above-mentioned Patent Document 4, the bale is expanded after compression, and the relatively shallow cap part (corresponding to the bottom part when packed into the bale) has an upward projection portion formed under the bale compression. That is, the bottom part has a raised bottom. The projection portion of the bottom part is folded back by the expansion force of the bale so as to become a recess portion, and the packing of the bale is finished (FIGS. 8 to 11).
In the case of this technology, the bag-base part needs to be molded in advance. The bag-base part is molded, and hence it cannot be stored in a stacked state, which is inconvenient for storage and transportation.
Moreover, the filter tow is fed into a compression box as a mass of a continuous pre-compressed fiber, but, after the bag-base part is installed in the compression box, there is a problem that the bag-base part may be removed from the installation part due to friction during insertion of the mass of the yarn body in the compression process. When the compression pressure applied onto the bale is removed, the raised bottom portion of the cap part (bottom part) is folded back by the expansion force of the bale so as to become the recess portion (downward projection portion), but during the expansion, a stress is applied to the cap part and the bag-base part, which might cause peeling-off of the seal or non-uniform expansion.
JP-A2005-528096 (Patent Document 5) discloses a technology in which a surface is smoothed by making an internal pressure of a bale negative by using means such as a vacuum pump in the above-mentioned Patent Documents 3 and 4. According to this document, as described in the above-mentioned Patent Documents 3, 4 and 5, a method for controlling expansion of a bale is proposed, the method involving heat-sealing a package (packing material) made of a plastic sheet or film, for example so as to seal the package, generating a negative pressure inside the bale with expansion of the bale, and, as a means of obtaining additional negative pressure, deaerating the inside of the bale so as to balance an atmospheric pressure with the rebound internal pressure of the bale.
That is, as described also in the above-mentioned Patent Document 5, after filter tow in a compressed state is sealed by airtight seal, an external pressure applied to the packed material is released. As a result, the material is expanded under an action of its own resilient recovering force inside of the package. Then, due to increase of a capacity of the package, a negative pressure is generated in the inside of the package. It is described that the package size is preferably selected so that the compressed filter tow cannot expand completely, that is, so that the filter tow inside the packaging material is still compressed to a certain degree inside the package even after its partial expansion. (paragraph [0021] of JP-A 2005-528096, corresponding to paragraph [0035] of US-A 2005/0161358).
As described above, if deaeration is to be performed, it is performed for the purpose of eliminating excess air inside the package in order to prevent full expansion of the compressed filter tow. It is also described that the minimum value of the negative pressure is 0.01 bar (claim 1). 0.01 bar corresponds to 1 kPa and is smaller than the above expansion force (rebound pressure) of the bale of 20 to 400 kPa, and the negative pressure does not have an effect to control the expansion of the bale. Patent Document 5 discloses a packing technology in which the bale is expanded till the stress by expansion of the bale package and the rebound pressure of the bale are balanced, and in this case, too, a large stress is applied to the heat-seal portion of the packaging material, and there is a problem that the seal portion or the like is fractured.
JP-A2006-517896 (Patent Document 6) discloses a tow packing system in which an evacuator is formed in the package having a 3-piece or 2-piece structure. This document discloses a technology for controlling excessive expansion of a bale by creating a large package wrapping around the bale by using two films for a top portion and a bottom portion and heat-sealing the four edges and removing the excess air through the evacuator so as to form an airtight package. In the case of the package form in which the two films are arranged and sealed to sandwich the bale from above and below the bale, the bale can be covered by the packaging material more easily, but a large excess portion is created in the packaging material (film) after packing the bale to increase an air taken-in amount.
Therefore, even with the increase of the internal capacity by natural expansion of the bale, the amount of excess air is larger than that, and generation of the negative pressure cannot be expected. Thus, in order to evacuate the excess air inside the packaging material and to generate the negative pressure, the air needs to be removed by a vacuum pump or the like. The large amount of air to be removed leads to poor working of efficiency. Even if the inside of the bale can be deaerated to the absolute vacuum as in the above-mentioned Patent Document 5, the resulting atmospheric pressure is only 100 kPa, which cannot control expansion of the bale, and there is a problem that the stress is still applied to the packaging material of the bale.
Further, a special packaging material in which an evacuator is installed needs to be prepared, and there is a problem that a cost of the packaging material is high. Moreover, other than the above problems in workability, there arises a problem that the left over portion needs to be stored neatly because a large quantity of film is left over after the packing. If the storage condition of the film excess portion is not satisfactory, the portion can become obstacles in stacking or transportation of the bale, or abrasion of the film excess portion might cause a pin hole, which results in loss of the internal pressure and causes expansion of the bale.